title: Formation of cysteine conjugates from dihydroxyphenylalanine and its S-cysteinyl derivatives by peroxidase-catalyzed oxidation.
abstract: Peroxidase-catalyzed oxidation of 3-(3,4-dihydroxyphenyl)alanine (DOPA) and its S-cysteinyl derivatives(cysteinyldopas) in the presence of cysteine was studied by analyzing the products with chromatography on Dowex 50W. Products of the oxidation of DOPA were found to be 5-S- and 2-S-cysteinyldopa, 2,5-S,S-dicysteinyldopa, and three unknown compounds A1, B, and C. 5-S- and 2-S-cysteinyldopa were also oxidized as easily as DOPA to give 2,5-S,S-dicysteinyldopa and similar patterns of the unknown compounds. Further oxidation of 2,5-S,S-dicysteinyldopa in the presence of cysteine yielded compounds A1, B, and C, whereas in its absence compound B was not formed. From these results coupled with the spectral data, it is suggested that compounds A1 and C are the two isomeric dihydrobenzothiazine derivatives of 2,5-S,S-dicysteinyldopa, while compound B is 2,5,6-S,S-tricysteinyldopa. These date suggest a possibility that peroxidase may play some role in the formation of cysteinyldopa and related metabolites in vivo.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D003545:Cysteine; D003548:Cysteinyldopa; D004295:Dihydroxyphenylalanine / Q000031:analogs & derivatives; D010084:Oxidation-Reduction; D010544:Peroxidases
chemical_list: D003548:Cysteinyldopa; D004295:Dihydroxyphenylalanine; D010544:Peroxidases; D003545:Cysteine